1. Field of the Invention
The present invention relates to an inspection optical system that is suitably used for inspection of optical characteristics of color filters incorporated in liquid crystal display devices and the like.
2. Description of Related Art
A color filter for a liquid crystal display device generally consists of three color filters including R, G, and B. In this specification, the range covered by one R filter, the range covered by one G filter, and the range covered by one B filter are each defined as one pixel.
Evaluations of optical characteristics of this color filter are carried out such that a light spot from a measurement light source is projected onto the center of one pixel of R, transmittance spectrum, chromaticity, white balance, etc. of the central area are measured. The same measurements are made on the pixels of G and B. The color filter to be measured is referred to as the “sample”.
FIG. 14 shows an irradiation spot (referred to as “irradiation spot U”) incident on one pixel (R pixel in this Figure).
As FIG. 14 shows, the irradiation spot U is smaller than the size of one pixel in conventional cases.
The reason that conventional measurements are carried out by projecting such an irradiation spot U smaller than the size of one pixel on a central area of the pixel is that the chromaticity/transmittance within the pixel of a color filter have been assumed to be approximately uniform.
However, recently, as the display screens of liquid crystal display devices become larger, the size of the pixel of a color filter becomes larger. With the increased size of pixel and changes in production process, the film thickness of the color filter within one pixel has become uneven as shown in a cross-sectional view of FIG. 15. Accordingly, unevenness in chromaticity/transmittance within the pixel of the color filter has been also pointed out, whereby the process of evaluating chromaticity/transmittance of a color filter needs to be reviewed.
In addition, only irradiation spots U with fixed sizes have been heretofore available.
In fact, since the pixel size of a color filter varies depending on the application of the products, the shape of the aperture that forms the irradiation spot needs to be changed accordingly.
In order to change the size of the irradiation spot U, it is necessary to replace the aperture unit inserted into the optical system, and readjustment of the optical system is required upon each replacement.
It is therefore an object of the present invention to provide an aperture variable inspection optical system that allows the size of the irradiation spot U to be changed without replacing the aperture unit.
It is another object of the present invention to provide a color filter evaluation process that enables inspection of optical characteristics of the entire area of one pixel of a color filter.